1. Statement of the Technical Field
The present invention relates to the transmission of encoded data in a radio signal, and more particularly to audio watermarking.
2. Description of the Related Art
The conventional radio frequency spectrum ranges from 30 kHz to 300 GHz and consists of very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF), ultra high frequency (UHF), SHF and EHF allocations for both civil and military applications. Though it cannot be said that the modern allocation of the conventional radio frequency spectrum had ever represented an adequate distribution of bandwidth able to satisfy the needs of all users, until recently, the modern allocation of the conventional radio frequency spectrum had served its purpose nonetheless. More recently, however, advancements in communications technologies have rendered the modern allocation unacceptable.
Specifically, there recently has arisen an acute need for accommodating a greater throughput of information within the presently limited allocation of radio spectrum available to both military and civilian users. In that regard, as advanced communications are developed for use within their respective presently allocated portion of the radio spectrum, a greater amount of information must flow within the allocated portion, even though the allocated portion is bandwidth limited. Thus, in the formation of an advanced communications system, incremental radio frequency spectrum slices will be required to accommodate the implementation of the system.
Yet, short of re-allocating the present bandwidth limited radio frequency spectrum to include a new spectrum slice, most new data transmission systems require dedicated radio spectrum that must be allocated or re-assigned from pre-existing concerns. Few who presently control a portion of the required spectrum, however, would be willing to relinquish control over their respective monetarily invaluable slice of the radio frequency spectrum. Consequently, the implementation of a new radio frequency communications technology will not be possible in many cases.
To address the inherent bandwidth limitations of the radio frequency spectrum several multiplexing techniques have been both proposed and implemented. In particular, within the wireless communications arts, multiplexing has become an essential technology with regard to the expansion of a pre-established and fixed width slice of the radio frequency spectrum. Several types of multiplexing schemes have been successfully deployed to facilitate such expansion, including Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA).
In all multiplexing cases, however, the use of multiplexing is hardware and software dependent upon the specific application. To that end, while multiplexing has been proven successful in the expansion of an allocated portion of the radio frequency spectrum to accommodate digital cellular voice and data traffic, the multiplexing solutions of digital cellular telephony are strictly limited to such application. To apply multiplexing to other forms of data exchange would require a ground-up design and implementation of an entirely new communications mechanism.
Notwithstanding, it would be preferable to be able to transmit auxiliary data over an existing communications link residing within an already allocated portion of the radio frequency spectrum. As an example, in the aviation arts “free flight” navigation systems have been proposed in which positional and environmental data regarding the position and placement of an aircraft in three-dimensional space can be collected by the aircraft and provided to remotely positioned entities, such as ground control operators. Importantly, the free flight navigation data can be provided from aircraft to ground without the assistance of radar. Consequently, an approximate if not accurate three-dimensional visualization of the position of the aircraft and its environment can be provided to the remotely positioned entity.
To enable the communication of free flight data from aircraft to remote entity, though, would require a separate communicative link between the aircraft and remote entity. Considering the limited allocation of radio frequency spectrum, however, it would seem that a truly effective free flight navigation system would not be possible without the cooperation of one or more stakeholders of the modern allocation of the radio frequency spectrum. In fact, in the similar circumstance of packet radio and third generation (3G) wireless technologies, the government of the United States indeed relinquished a significant portion of the radio frequency spectrum then allocated for military use. Yet, at present it does not seem realistic to expect the government of the United States to continue to relinquish control over its allocated portion of the radio frequency spectrum to accommodate every emerging technology requiring bandwidth in the radio frequency spectrum.
Analogously, in the technical space of multimedia broadcasting and distribution, advances in technology have led to the development of systems for controlling the distribution and use of multimedia works, such as music, video and the like. These technological advances, however, like free flight navigation, require either a significant increase in radio frequency bandwidth to accommodate additional data used in the course of implementing content distribution control technologies. In particular, content limiting data must be included with the multimedia work upon its distribution, thereby dramatically increasing the size of the deliverable which would then include both the multimedia content itself, in addition to the control data. As before, though, it would not be expected that a controlling entity would relinquish portions of allocated bandwidth in support of the implementation of content distribution technologies.
As a result, while many have abandoned attempts at implementing content distribution control technologies, some notable efforts persist. Examples include multimedia watermarking, and more particularly, audio watermarking. To implement multimedia watermarking over the wireless radio frequency medium, it has been suggested that the watermarking data ought to be broadcast simultaneous with the multimedia payload in a spread spectrum manner. In this regard, by spreading broadcast components of the data across a multiplicity of broadcast frequencies, the ability of one to individually detect a component portion of the transmission would be reduced to a near impossibility. Unfortunately, spread spectrum watermarking techniques limit the volume of control data to a pittance barely adequate to carry basic copyright information.